Alfvenic Heating of disks and accretion columns of Classical T Tauri Stars

Details Alfvenic Heating of disks and accretion columns of Classical T Tauri Stars Alfvenic Heating of disks and accretion columns of Classical T Tauri Stars

Jan 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt..........v&link_type=abstract

PhD Thesis, Departamento de Astronomia, Universidade de São Paulo, SP, Brazil, 2001.

Astronomy and Astrophysics

Astronomy

1

Scientific paper

In this work, we investigate the role that Alfvenic heating plays on protostellar accretion disks and in the magnetic funnels of gas that connect the accretion disk to the surface of a Classical T Tauri star. In order to quantify it, we analyze the damping of Alfvén waves taking into account the intrinsic properties of each one of those environments. The Alfvenic heating on protostellar accretion disks was treated into the standard accretion disk approximation (Pringle 1981) and also into the layered model of Gammie (1996). For both models, two damping mechanisms were studied: nonlinear and turbulent. We derive damping lengths, heating rates and energy fluxes, all of them related to the dissipation of the Alfvén wave modes as a function of the disk density, temperature and magnetic field intensity. The results show us that Alfvenic heating contributes to the temperature increase of the disk gas, mainly if the damping mechanism is turbulent. For the magnetic funnels of T Tauri stars, we studied four damping mechanisms: nonlinear, turbulent, collisional and viscous-resistive. We use the magnetospheric accretion model by Hartmann, Hewett & Calvet (1994), but adopting an ad hoc temperature profile slightly different that, however, still fits the observations. We consider two different hypothesis for the generation of Alfvén waves. Firstly, the waves are generated at the surface of the star; then, the waves are generated locally, throughout the tube. Despite the place where they are formed, Alfvén waves are quickly and locally damped. We also analyze thermal conduction in the tube and found it to be very low, unable to transport the locally generated Alfvenic energy to more distant regions. Taking this into account, we conclude that when Alfvén waves are generated locally they can be responsible for the high temperatures obtained from observations. In this case, the degree of turbulence related to the waves is constrained and we found that it doesn't need to be very high to generate the desired heating rates.

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